Optical system for use in single lens reflex cameras

ABSTRACT

An optical system for a viewfinder camera is provided. The objective lens system is divided into at least two separate lens groups. The first lens group provides an insufficient correction to aberration while the second lens group is designed specifically to correct the aberration transmitted through the first lens group. The complimentary viewfinder system is also likewise designed to correct the same aberration as the second lens group.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical system for use in asingle-lens reflex camera, and more particularly, it pertains to asingle-lens reflex camera optical system which includes a beam pathsplitter inside a photographing lens optical system, as in a motionpicture camera and a compact single-lens reflex camera, so that aphotographer can obtain through a view finder system a light split bythe beam path splitter after having passed through a lens group locatedbefore the beam path splitter toward an object.

2. Description of the Prior Art

Until now for this type of single-lens reflex camera optical system, aphotographing lens optical system, i.e., the most important element of acamera, is first designed to achieve the best corrected aberration toensure high image forming performance on a film surface. A view findersystem is then designed in consideration of aberration conditions of thelens group on the object side of a beam path splitter in thephotographing lens optical system so that a favorable finder image canbe obtained. As is widely known, however, a view finder system consistsmainly of a combination of positive lens elements. This causes the viewfinder system itself to produce longitudinal aberration when theconstruction is simplified. Therefore, even if the lens group, locatedbefore the beam path splitter, is achromatized, longitudinal chromaticaberration occurs in a finder image on the focal plane. To obtain afavorable finder image accordingly, the longitudinal chromaticaberration must be corrected inside the view finder system, which, as aresult, requires a specific number of elements for an achromatic lens,thus causing the entire optical system for a single-lens reflex camerato become a considerably complex lens construction.

U.S. Pat. No. 3,583,785 and U.S. Pat. No. 4,086,000 are cited of generalinterest.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide an opticalsystem for use in a single-lens reflex camera, which obviates the abovedrawback and is simple in optical construction, as a whole.

According to the present invention, both a photographing lens opticalsystem and a view finder optical system are designed in closerelationship to each other, the photographing lens optical system beingmaintained equal in optical construction to the conventional system,while the view finder optical system is simplified, thereby contributingto the simplification of an entire optical system for a single-lensreflex camera.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a schematic cross sectional view of an optical systemfor explaining the concept of the present invention.

FIG. 2 represents a schematic cross sectional view of a first embodimentof the present invention.

FIG. 3 represents a schematic cross sectional view of an exemplary priorart.

FIG. 4 represents a schematic cross sectional view of a part of a secondembodiment of the present invention.

FIG. 5 represents a schematic cross sectional view of a part of a thirdembodiment of the present invention.

FIG. 6 represents a schematic cross sectional view of a part of a fourthembodiment of the present invention.

FIGS. 7a to 7d represents graphic plots of various aberrations of theobjective lens system in the first embodiment.

FIGS. 8a to 8c represent graphic plots of various aberrations of thefinder system in the first embodiment.

FIGS. 9a to 9d represent graphic plots of various aberrations of theobjective lens system in the exemplary prior art.

FIGS. 10a to 10c represent graphic plots of various aberrations of thefinder system in the exemplary prior art.

FIGS. 11a to 11c represent graphic plots of various aberrations of thefinder system in the second embodiment.

FIGS. 12a to 12c represent graphic plots of various aberrations of thefinder system in the third embodiment.

FIGS. 13a to 13c represent graphic plots of various aberrations of thefinder system in the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description will now be given of the present invention according to theembodiments shown in the drawings. FIG. 1 shows a schematic view of oneembodiment of the present invention for a motion picture camera with abuilt-in zoom lens system. With reference to FIG. 1, portions 1 and 3together constitute a photographing lens optical system for focusing anobject on a film surface 4. Provided inside the photographing lensoptical system is a beam path splitter 2 consisting of a half mirrordisposed between a first lens group 1 and a second lens group 3. Firstlens group 1 consists of a focal zoom lens system which is of the priorart optical construction. However, first lens group 1 sets aberrationsaccording to the features of the present invention so that thelongitudinal chromatic aberration may be corrected in excess inside thelens group. This aberration setting is possible by means of the priorart design technique. Second lens group 3 consists of a master lenssystem. As is well known, the master lens system has a positiverefraction which causes longitudinal chromatic aberration to occurinside the system. According to ordinary design, the longitudinalchromatic aberration is corrected therein by using a required number oflens elements for achromatism in the master lens system. According tothe features of the present invention, however, the longitudinalchromatic aberration is overcorrected or corrected in excess inside thefirst lens group 1. This causes the correction excess in the first lensgroup 1 to offset the longitudinal chromatic aberration occurring in thesecond lens group 3 which is the master lens system. Therefore, thecorrection of longitudinal chromatic aberration in the second lens group3 is eliminated, whereby the number of lens elements required inside thesecond lens group 3 can be reduced from the conventional system.

According to the present invention, it is natural that longitudinalchromatic aberration is required to be corrected in excess inside thefirst lens group 1. This causes the first lens group 1 to require alarger number of elements than the conventional system. In other words,the present invention features the entire optical system for aphotographing lens wherein the number of elements required for thesecond lens group 3 of the conventional system has been transferred tothe first lens group 1. Therefore, as far as the photographing lensoptical system is concerned, the number of elements is equal to theconventional system without any simplification in optical construction.In addition, aberration performance is equal between the photographinglens optical system according to the present invention and theconventional one.

Referring again to FIG. 1, view finder systems are labeled 5, 6 and 7.The light passing through the first lens group 1 which is the zoom lenssystem in the photographing lens optical system is split by beam pathsplitter 2 and focused as primary image 8 by objective lens systemshaving positive refraction. Primary image 8 is further focused on focalplane 9 as a secondary image by erect lens system 6 with positiverefraction. A virtual image of the secondary image on focal plane 9 isthen observed through eyepiece system 7 by eye 10 of a photographer. Asis clear from the foregoing, the optical system up to focal plane 9 inthe view finder system consists mainly of a positive lens elementcombination and longitudinal chromatic aberration occurs in an image onfocal plane 9. According to ordinary design, the longitudinal chromaticaberration is corrected inside the view finder system, which must use arequired number of lens elements for an image, whose longitudinalchromatic aberration has been corrected, to be focused on focal plane 9.In contrast, according to the features of the present invention, thelongitudinal chromatic aberration is corrected in the excess in firstlens group 1 of the photographing lens optical system, wherebylongitudinal chromatic aberration occurring in positive lens elements 5and 6 of the view finder system is offset by the correction in excess.Therefore, the correction of longitudinal chromatic aberration occurringin the view finder system lens elements 5 and 6 in relation to an imagefocused on focal plane 9 is eliminated, whereby the number of lenselements required inside the view finder system can be reduced from theconventional system. Thus, the number of lens elements for the entireoptical system for a single-lens reflex camera can be decreased.

Until now a photographing lens optical system and a view finder systemare designed independently of each other, and longitudinal chromaticaberrations occurring in the master lens system and view finder systemof the photographing lens optical system which is originally thepositive lens system are separately corrected in the respective systems.In contrast, the present invention simplifies construction of the entireoptical system for a single-lens reflex camera by concentrating theburden of aberration correction on the lens group located before thebeam path splitter toward an object.

It should be noted that in FIG. 1, the first lens group 1 is notrequired to consist of a focal zoom lens system alone and may consist ofa combination of the zoom lens system and part of the lens elements inthe master lens system next to the zoom lens system. In this case, beampath splitter 2 is arranged inside the master lens system. In addition,if beam path splitter 2 is a movable mirror replaced for a half mirror,the embodiment in FIG. 1 may be used as an optical system for a compactstill camera. It is to be understood that although description was madeof longitudinal chromatic aberration alone, the technological concept ofthe present invention is, needless to say, applicable to otheraberrations.

FIG. 2 shows a first embodiment of the present invention. Objective lenssystem is constructed by an object side part 1 and an image side part 3,an image forming light path being passed through the object side andimage side parts 1 and 3 toward image 4. The image forming light path isbranched between the object side part 1 and the image side part 3 bysemitransparent mirror 2 of the prism P. The branched light path isreceived by a branch optical system including elements 5, 6, 9 and 7,which forms a finder system in combination with the object side part 1of the objective lens system. The front lens group 5 serves as anobjective of the branch optical system, and the intermediate lens group6 serves as an erecting system for converting the inverted primary realimage formed by the front lens group 5 into an erecting secondary realimage on the reticle at the eye side of the focusing plate 9. Finally,the rear lens group 7 serves as an ocular for watching the image on thereticle.

Table 1-L shows a lens construction of the objective lens system alongthe light path from an object to the image 4 in FIG. 2. Table 1-F showsa lens construction of the finder system along the light path from anobject to the eye 10 in FIG. 2.

                  TABLE 1-L                                                       ______________________________________                                        (Embodiment 1-L)                                                              f = 33.00  F.sub.No. = 1.26  2 = 12°  L.B = 5.68                       Radius of      Axial    Refractive Abbe                                       Curvature      Distance Index      Number                                     ______________________________________                                                   r.sub.1                                                                             78.512  d.sub.1                                                                           1.5                                              L.sub.1                           N.sub.1                                                                            1.80518                                                                             ν.sub.1                                                                        25.43                                   r.sub.2                                                                             33.152  d.sub.2                                                                           1.5                                                         r.sub.3                                                                             38.724  d.sub.3                                                                           6.2                                              L.sub.2                           N.sub.2                                                                            1.64050                                                                             ν.sub.2                                                                        60.08                                   r.sub.4                                                                             ∞ d.sub.4                                                                           0.1                                                         r.sub.5                                                                             26.281  d.sub.5                                                                           6.9                                              L.sub.3                           N.sub.3                                                                            1.64050                                                                             ν.sub.3                                                                        60.08                                   r.sub.6                                                                             169.775 d.sub.6                                                                           17.7                                                        r.sub.7                                                                             123.964 d.sub.7                                                                           1.0                                              L.sub.4                           N.sub.4                                                                            1.64050                                                                             ν.sub.4                                                                        60.08                                   r.sub.8                                                                             9.026   d.sub.8                                                                           4.4                                                         r.sub.9                                                                             -30.992 d.sub.9                                                                           0.9                                              L.sub.5                           N.sub.5                                                                            1.56873                                                                             ν.sub.5                                                                        63.1                                    r.sub.10                                                                            22.881  d.sub.10                                                                          0.6                                                         r.sub.11                                                                            17.214  d.sub.11                                                                          2.2                                              L.sub.6                           N.sub.6                                                                            1.80518                                                                             ν.sub.6                                                                        25.43                                   r.sub.12                                                                            39.676  d.sub.12                                                                          0.8                                                         r.sub.13                                                                            28.000  d.sub.13                                                                          4.2                                              L.sub.7                           N.sub.7                                                                            1.62041                                                                             ν.sub.7                                                                        60.29                                   r.sub.14                                                                            -13.300 d.sub.14                                                                          1.0                                              L.sub.8                           N.sub.8                                                                            1.73300                                                                             ν.sub.8                                                                        28.24                                   r.sub.15                                                                            -64.057 d.sub.15                                                                          6.3                                                         r.sub.16                                                                            ∞ d.sub.16                                                                          7.0                                              P                                 N.sub.9                                                                            1.62588                                                                             ν.sub.9                                                                        35.70                                   r.sub.17                                                                            ∞ d.sub.17                                                                          3.5                                                         r.sub.18                                                                            26.419  d.sub.18                                                                          2.0                                              L.sub.9                           N.sub.10                                                                           1.64050                                                                             ν.sub.10                                                                       60.08                                   r.sub.19                                                                            -39.539 d.sub.19                                                                          0.2                                                         r.sub.20                                                                            20.518  d.sub.20                                                                          3.5                                              L.sub.10                          N.sub.11                                                                           1.62135                                                                             ν.sub.11                                                                       61.28                                   r.sub.21                                                                            71.826  d.sub.21                                                                          1.5                                                         r.sub.22                                                                            -26.604 d.sub.22                                                                          3.0                                              L.sub.11                          N.sub.12                                                                           1.74000                                                                             ν.sub.12                                                                       28.26                                   r.sub.23                                                                            -168.070                                                                              d.sub.23                                                                          1.5                                                         r.sub.24                                                                            -974.393                                                                              d.sub.24                                                                          3.6                                              L.sub.12                          N.sub.13                                                                           1.64050                                                                             ν.sub.13                                                                       60.08                                   r.sub.25                                                                            -73.788 d.sub.25                                                                          0.2                                                         r.sub.26                                                                            19.202  d.sub.26                                                                          3.5                                              L.sub.13                          N.sub.14                                                                           1.64050                                                                             ν.sub.14                                                                       60.08                                   r.sub.27                                                                            39.469                                                       ______________________________________                                    

                  TABLE 1-F                                                       ______________________________________                                        (Embodiment 1-F)                                                              (f = 33.00)  Diopter = 0.0  Magnification = 2.33                              Radius of      Axial     Refractive Abbe                                      Curvature      Distance  Index      Number                                    ______________________________________                                                   r.sub.1                                                                              78.512 d.sub.1                                                                            1.5                                             L.sub.1                            N.sub.1                                                                            1.80518                                                                             ν.sub.1                                                                        25.43                                  r.sub.2                                                                              33.152 d.sub.2                                                                            1.5                                                        r.sub.3                                                                              38.724 d.sub.3                                                                            6.2                                             L.sub.2                            N.sub.2                                                                            1.64050                                                                             ν.sub.2                                                                        60.08                                  r.sub.4                                                                              ∞                                                                              d.sub.4                                                                            0.1                                                        r.sub.5                                                                              26.281 d.sub.5                                                                            6.9                                             L.sub.3                            N.sub.3                                                                            1.64050                                                                             ν.sub.3                                                                        60.08                                  r.sub.6                                                                              169.775                                                                              d.sub.6                                                                            17.7                                                       r.sub.7                                                                              123.964                                                                              d.sub.7                                                                            1.0                                             L.sub.4                            N.sub.4                                                                            1.64050                                                                             ν.sub.4                                                                        60.08                                  r.sub.8                                                                              9.026  d.sub.8                                                                            4.4                                                        r.sub.9                                                                              -30.992                                                                              d.sub.9                                                                            0.9                                             L.sub.5                            N.sub.5                                                                            1.56873                                                                             ν.sub.5                                                                        63.1                                   r.sub.10                                                                             22.881 d.sub.10                                                                           0.6                                                        r.sub.11                                                                             17.214 d.sub.11                                                                           2.2                                             L.sub.6                            N.sub.6                                                                            1.80518                                                                             ν.sub.6                                                                        25.43                                  r.sub.12                                                                             39.676 d.sub.12                                                                           0.8                                                        r.sub.13                                                                             28.000 d.sub.13                                                                           4.2                                             L.sub.7                            N.sub.7                                                                            1.62041                                                                             ν.sub.7                                                                        60.29                                  r.sub.14                                                                             -13.300                                                                              d.sub.14                                                                           1.0                                             L.sub.8                            N.sub.8                                                                            1.73300                                                                             ν.sub.8                                                                        28.24                                  r.sub.15                                                                             -64.057                                                                              d.sub.15                                                                           6.3                                                        r.sub.16                                                                             ∞                                                                              d.sub.16'                                                                          11.5                                            P'                                 N.sub.9                                                                            1.62588                                                                             ν.sub.9                                                                        35.70                                  r.sub.17'                                                                            ∞                                                                              d.sub.27                                                                           18.0                                                       r.sub.28                                                                             17.000 d.sub.28                                                                           5.0                                             L.sub.14                           N.sub.15                                                                           1.62041                                                                             ν.sub.15                                                                       60.29                                  r.sub.29                                                                             -11.000                                                                              d.sub.29                                                                           2.0                                             L.sub.15                           N.sub.16                                                                           1.73300                                                                             ν.sub.16                                                                       28.24                                  r.sub.30                                                                             -69.700                                                                              d.sub.30                                                                           43.2                                                       r.sub.31*                                                                            20.000 d.sub.31                                                                           4.0                                             L.sub.16                           N.sub.17                                                                           1.49140                                                                             ν.sub.17                                                                       57.9                                   r.sub.32*                                                                            -20.000                                                                              d.sub.32                                                                           42.3                                                       r.sub.33*                                                                            20.000 d.sub.33                                                                           4.0                                             L.sub.17                           N.sub.18                                                                           1.49140                                                                             ν.sub.18                                                                       57.9                                   r.sub.34*                                                                            -20.000                                                                              d.sub.34                                                                           16.9                                                       r.sub.35                                                                             ∞                                                                              d.sub.35                                                                           4.0                                             G                                  N.sub.19                                                                           1.49140                                                                             ν.sub.19                                                                       57.9                                   r.sub.36                                                                             ∞                                                                              d.sub.36                                                                           21.1                                                       r.sub.37                                                                             25.700 d.sub.37                                                                           5.0                                             L.sub.18                           N.sub.20                                                                           1.62041                                                                             ν.sub.20                                                                       60.29                                  r.sub.38                                                                             -10.500                                                                              d.sub.38                                                                           1.0                                             L.sub.19                           N.sub.21                                                                           1.73300                                                                             ν.sub.21                                                                       28.24                                  r.sub.39                                                                             -23.000                                                                              d.sub.39                                                                           18.0                                            Eye Point                                                                     ______________________________________                                         *ε = -1.35, iΣ Ciφ.sup.2i = 0    Between Tables 1-L and     1-F, the construction from r.sub.1 to r.sub.15 is identical with each     other. Further, prism P in Table 1-L is substantially identical with prism     P' in Table 1-F, except for the effective thickness, i.e., r.sub.1- to     r.sub.17 in case of Table 1-L, and r.sub.16 to r'.sub.17 in case of Table     1-F, which difference is caused by the light path branching from the     semitransparent mirror 2.

According to Table 1-L or 1-F, the object side part 1, i.e., the lensconstruction from r₁ to r₁₅, shows an excessive correction oflongitudinal chromatic aberration of F-line to d-line, -0.43 diopter, interms of finder. On the contrary, the final longitudinal chromaticaberration of F-line to d-line of the whole objective lens system atfilm 4 is +0.026 mm. This means that the excessive correction oflongitudinal chromatic aberration in the object side part 1 is cancelledwith the undercorrected or insufficient correction of the same in theimage side part 3.

On the other hand, the branch optical system 5 to 7 in the finder systemhas an undercorrected insufficiently corrected longitudinal chromaticaberration of F-line to d-line, +0.55 diopter, by itself. Thisinsufficient correction of longitudinal chromatic aberration iscancelled with the excessive correction of the same in the object sidepart 1 of the objective lens system, and the longitudinal chromaticaberration of F-line to d-line of the whole finder system, i.e., theobject side part 1 plus the branch optical system, is -0.07 diopter. Inaddition, the longitudinal chromatic aberration of F-line to d-line ofthe whole finder system at the reticle of focusing plate 9 is +0.030 mm.

According to the general requirement for an objective lens system, theabsolute value for the longitudinal chromatic aberration of F-line tod-line should be less than about 0.07 mm. The objective lens system ofthe present invention fulfills this requirement as a whole lens systemand also has a characteristic image side part 3 of an insufficientlycorrected longitudinal chromatic aberration to be cancelled with theexcessive correction of the same in the image side part 1. The degree ofthe insufficiency of the correction for the longitudinal chromaticaberration in the image side part 3 thus characterizes the presentinvention, i.e., the absolute value for the insufficient correction ofthe longitudinal chromatic aberration of F-line to d-line of the imageside part 3 is greater than 0.0004 f_(R) according to the presentinvention, wherein f_(R) represents the focal length of the image sidepart 3.

In other words, the present invention is also characterized by theabsolute value of the excessive correction of longitudinal chromaticaberration of F-line to d-line in the object side part 1 of theobjective lens system, which absolute value is greater than 0.3 diopterin terms of finder. In case of the embodiment in FIG. 2, such anexcessive correction for longitudinal chromatic aberration is mainlycaused by the doublet composed of lens elements L₇ and L₈.

The ocular, or the rear lens group, 7 of the branch optical system inFIG. 2 adopts a doublet for correcting the chromatic aberration, whichwould otherwise occur at the ocular itself, to prevent the bluecoloration of the inner edge of the finder frame. Another doublet isalso adopted as the objective, or the front lens group, 5 of the branchoptical system. The pair of doublets 5 and 7 make the branch opticalsystem symmetric to prevent the occurrence of lateral chromaticaberration in the finder image.

In the erecting system 6 of the branch optical system, a pair ofidentically shaped single lenses are adopted, each of the single lensesbeing a symmetric lens formed by aspherical surfaces to correct thefield curvature of the finder image. In Table 1-F, the asphericalsurface is indicated by a star (*), e.g., r₃₁ *, and the necessaryinformation of the aspherical surface are given at the bottom of Table1-F. An aspherical surface is generally given by the following formula:##EQU1## Wherein C₀ represents the radius of curvature of the asphericalsurface at the optical axis,

φ represents the distance from the optical axis,

χ represents the displacement of the aspherical surface from thespherical surface of radius of curvature C₀ in the direction of theoptical axis,

and ε and C_(i) represent various coefficients for determining theaspherical surface.

Table 1-F shows that all aspherical surfaces r₃₁ * to r₃₄ * areidentical, and ε is -1.35 and C₁, C₂, C₃ - - - are all zero in the aboveformula (1).

By the way, the identical aspherical surface can be given by anotherexpression when C₁, C₂, C₃ - - - are all zero in the formula (1), theexpression being: ##EQU2## Thus, the aspherical surfaces of Table 1-Fcan also be expressed in a form that Σ_(i) C_(i) φ^(2i) is not zero.

The above explanation for the expression of the aspherical surface canbe applied to other embodiments of the present invention, and furtherexplanation will be omitted.

As already mentioned, in the branch optical system of FIG. 2, thelongitudinal chromatic aberration is left in an insufficiently correctedcondition to avoid any addition of further lens elements and to simplifythe lens construction of the branch optical system.

FIGS. 7a to 7d represent the various aberrations of the lens system ofthe first embodiment in FIG. 2, and FIGS. 8a to 8c correspond to thosefor the finder system. These figures prove that the first embodiment inFIG. 2 is a highly useful and practical system.

FIG. 3 shows an exemplary prior art, the lens construction of theobjective lens system and the finder system being shown in Tables 2-Land 2-F, respectively.

                  TABLE 2-L                                                       ______________________________________                                        (Exemplary Prior Art - L)                                                     f = 33.00  F.sub.No. = 1.26  2 = 12°  L.B. = 12.29                     Radius of      Axial    Refractive Abbe                                       Curvature      Distance Index      Number                                     ______________________________________                                                   r.sub.1                                                                             78.512  d.sub.1                                                                           1.5                                              L.sub.1                           N.sub.1                                                                            1.80518                                                                             ν.sub.1                                                                        25.43                                   r.sub.2                                                                             33.152  d.sub.2                                                                           1.5                                                         r.sub.3                                                                             38.724  d.sub.3                                                                           6.2                                              L.sub.2                           N.sub.2                                                                            1.64050                                                                             ν.sub.2                                                                        60.08                                   r.sub.4                                                                             ∞ d.sub.4                                                                           0.1                                                         r.sub.5                                                                             26.281  d.sub.5                                                                           6.9                                              L.sub.3                           N.sub.3                                                                            1.64050                                                                             ν.sub.3                                                                        60.08                                   r.sub.6                                                                             169.775 d.sub.6                                                                           17.7                                                        r.sub.7                                                                             123.964 d.sub.7                                                                           1.0                                              L.sub.4                           N.sub.4                                                                            1.64050                                                                             ν.sub.4                                                                        60.08                                   r.sub.8                                                                             9.026   d.sub.8                                                                           4.4                                                         r.sub.9                                                                             -30.992 d.sub.9                                                                           0.9                                              L.sub.5                           N.sub.5                                                                            1.56873                                                                             ν.sub.5                                                                        63.10                                   r.sub.10                                                                            22.881  d.sub.10                                                                          0.6                                                         r.sub.11                                                                            17.214  d.sub.11                                                                          2.2                                              L.sub.6                           N.sub.6                                                                            1.80518                                                                             ν.sub.6                                                                        25.43                                   r.sub.12                                                                            39.676  d.sub.12                                                                          0.8                                                         r.sub.13                                                                            50.653  d.sub.13                                                                          3.2                                              L.sub.7                           N.sub.7                                                                            1.70030                                                                             ν.sub.7                                                                        47.67                                   r.sub.14                                                                            -62.704 d.sub.14                                                                          8.3                                                         r.sub.15                                                                            ∞ d.sub.15                                                                          7.0                                              P                                 N.sub.8                                                                            1.62588                                                                             ν.sub.8                                                                        35.70                                   r.sub.16                                                                            ∞ d.sub.16                                                                          3.5                                                         r.sub.17                                                                            15.872  d.sub.17                                                                          2.0                                              L.sub.8                           N.sub.9                                                                            1.64050                                                                             ν.sub.9                                                                        60.08                                   r.sub.18                                                                            36.085  d.sub.18                                                                          0.1                                                         r.sub.19                                                                            30.865  d.sub.19                                                                          3.3                                              L.sub.9                           N.sub.10                                                                           1.62135                                                                             ν.sub.10                                                                       61.28                                   r.sub.20                                                                            155.809 d.sub.20                                                                          1.1                                                         r.sub.21                                                                            - 22.817                                                                              d.sub.21                                                                          3.0                                              L.sub.10                          N.sub.11                                                                           1.74000                                                                             ν.sub.11                                                                       28.26                                   r.sub.22                                                                            16.622  d.sub.22                                                                          1.6                                                         r.sub.23                                                                            36.602  d.sub.23                                                                          0.8                                              L.sub.11                          N.sub.12                                                                           1.67270                                                                             ν.sub.12                                                                       32.22                                   r.sub.24                                                                            24.764  d.sub.24                                                                          2.8                                              L.sub.12                          N.sub.13                                                                           1.67790                                                                             ν.sub.13                                                                       55.38                                   r.sub.25                                                                            -17.259 d.sub.25                                                                          0.1                                                         r.sub.26                                                                            16.271  d.sub.26                                                                          3.5                                              L.sub.13                          N.sub.14                                                                           1.64050                                                                             ν.sub.14                                                                       60.08                                   r.sub.27                                                                            685.641                                                      ______________________________________                                    

                  TABLE 2-F                                                       ______________________________________                                        (Exemplary Prior Art - F)                                                     (f = 33.00)  Diopter = 0.0  Magnification = 2.43                              Radius of      Axial     Refractive Abbe                                      Curvature      Distance  Indent     Number                                    ______________________________________                                                   r.sub.1                                                                              78.512 d.sub.1                                                                            1.5                                             L.sub.1                            N.sub.1                                                                            1.80518                                                                             ν.sub.1                                                                        25.43                                  r.sub.2                                                                              33.152 d.sub.2                                                                            1.5                                                        r.sub.3                                                                              38.724 d.sub.3                                                                            6.2                                             L.sub.2                            N.sub.2                                                                            1.64050                                                                             ν.sub.2                                                                        60.08                                  r.sub.4                                                                              ∞                                                                              d.sub.4                                                                            0.1                                                        r.sub.5                                                                              26.281 d.sub.5                                                                            6.9                                             L.sub.3                            N.sub.3                                                                            1.64050                                                                             ν.sub.3                                                                        60.08                                  r.sub.6                                                                              169.775                                                                              d.sub.6                                                                            17.7                                                       r.sub.7                                                                              123.964                                                                              d.sub.7                                                                            1.0                                             L.sub.4                            N.sub.4                                                                            1.64050                                                                             ν.sub.4                                                                        60.08                                  r.sub.8                                                                              9.026  d.sub.8                                                                            4.4                                                        r.sub.9                                                                              -30.992                                                                              d.sub.9                                                                            0.9                                             L.sub.5                            N.sub.5                                                                            1.56873                                                                             ν.sub.5                                                                        63.1                                   r.sub.10                                                                             22.881 d.sub.10                                                                           0.6                                                        r.sub.11                                                                             17.214 d.sub.11                                                                           2.2                                             L.sub.6                            N.sub.6                                                                            1.80518                                                                             ν.sub.6                                                                        25.43                                  r.sub.12                                                                             39.676 d.sub.12                                                                           0.8                                                        r.sub.13                                                                             50.653 d.sub.13                                                                           3.2                                             L.sub.7                            N.sub.7                                                                            1.70030                                                                             ν.sub.7                                                                        47.67                                  r.sub.14                                                                             -62.704                                                                              d.sub.14                                                                           8.3                                                        r.sub.15                                                                             ∞                                                                              d.sub.15'                                                                          11.5                                            P'                                 N.sub.8                                                                            1.62588                                                                             ν.sub.8                                                                        35.70                                  r.sub.16'                                                                            ∞                                                                              d.sub.27                                                                           6.8                                                        r.sub.28                                                                             45.455 d.sub.28                                                                           5.3                                             L.sub.14                           N.sub.15                                                                           1.62280                                                                             ν.sub.15                                                                       56.98                                  r.sub.29                                                                             -9.823 d.sub.29                                                                           5.0                                             L.sub.15                           N.sub.16                                                                           1.68300                                                                             ν.sub.16                                                                       31.52                                  r.sub.30                                                                             -29.147                                                                              d.sub.30                                                                           38.9                                                       r.sub.31                                                                             -687.999                                                                             d.sub.31                                                                           4.5                                             L.sub.16                           N.sub.17                                                                           1.49140                                                                             ν.sub.17                                                                       57.9                                   r.sub.32                                                                             -14.000                                                                              d.sub.32                                                                           39.2                                                       r.sub.33                                                                             30.682 d.sub.33                                                                           1.0                                             L.sub.17                           N.sub.18                                                                           1.73300                                                                             ν.sub.18                                                                       28.24                                  r.sub.34                                                                             9.700  d.sub.34                                                                           3.0                                             L.sub.18                           N.sub.19                                                                           1.62280                                                                             ν.sub.19                                                                       56.98                                  r.sub.35                                                                             -26.234                                                                              d.sub.35                                                                           17.0                                                       r.sub.36                                                                             16.227 d.sub.36                                                                           3.0                                             L.sub.19                           N.sub.20                                                                           1.49140                                                                             ν.sub.20                                                                       57.9                                   r.sub.37                                                                             211.100                                                                              d.sub.37                                                                           13.4                                                       r.sub.38                                                                             ∞                                                                              d.sub.38                                                                           4.0                                             G                                  N.sub.21                                                                           1.49140                                                                             ν.sub.21                                                                       57.9                                   r.sub.39                                                                             ∞                                                                              d.sub.39                                                                           4.7                                                        r.sub.40                                                                             -51.853                                                                              d.sub.40                                                                           4.0                                             L.sub.20                           N.sub.22                                                                           1.49140                                                                             ν.sub.22                                                                       57.9                                   r.sub.41                                                                             -13.925                                                                              d.sub.41                                                                           14.4                                                       r.sub.42                                                                             21.598 d.sub.42                                                                           1.0                                             L.sub.21                           N.sub.23                                                                           1.73300                                                                             ν.sub.23                                                                       28.24                                  r.sub.43                                                                             8.311  d.sub.43                                                                           4.3                                             L.sub.22                           N.sub.24                                                                           1.62280                                                                             ν.sub.24                                                                       56.98                                  r.sub.44                                                                             -31.397                                                                              d.sub.44                                                                           15.0                                            Eye Point                                                                     ______________________________________                                    

In the exemplary prior art, the objective lens system is conventionallydesigned, i.e., the longitudinal chromatic aberration (F-line to d-line)in the object side part 1 is +0.23 diopter in terms of finder, and thefinal longitudinal chromatic aberration (F to d) in the whole objectivelens system at film 4 is -0.043 mm. This means that the inherentlongitudinal chromatic aberration of the image side part 3 issufficiently corrected within the image side part 3 by itself. In caseof the exemplary prior art, such a correction is mainly due to thedoublet composed of L₁₁ and L₁₂.

As apparent from the comparison between the first embodiment of thepresent invention and the exemplary prior art, the final longitudinalchromatic aberration at film 4 is substantially of the same degree andthe number of lens elements required to construct the objective lenssystem is identical with each other. Therefore, the objective lenssystem of the present invention is equivalent to the prior art as far asthe final result with which the objective lens system by itself isconcerned.

However, any simplified branch optical system such as in FIG. 2 cannotbe combined with the objective lens system of the exemplary prior art inFIG. 3. The longitudinal chromatic aberration is left in aninsufficiently corrected condition in the branch optical system of FIG.2, and this insufficient correction would not be improved by any meansand would remain in the final image in case of a finder system made bycombining the simplified branch optical system of FIG. 2 with theconventional object side part 1 of FIG. 3.

Therefore, the exemplary prior art in FIG. 3 inevitably adopts a branchoptical system in which the number of elements is increased to correctthe inherent longitudinal chromatic aberration of the branch opticalsystem by itself. According to Table 2-F, the longitudinal chromaticaberration (F-d) of the branch optical system by itself is -0.39diopter, and the longitudinal chromatic aberration (F-d) of the wholefinder system is -0.023 diopter. In addition, the longitudinal chromaticaberration (F-d) of the whole finder system at the reticle of focusingplate 9 is -0.049 mm. FIGS. 9a to 9d and 10a to 10c show various otheraberrations of the exemplary prior art.

As apparent from the above comparison, the present inventionsuccessfully provides an optical system for use in single lens reflexcameras in which the construction of the whole system is simplified withnecessary aberration corrections sufficiently achieved.

FIGS. 4 to 6 show finder systems of second to fourth embodiments of thepresent invention, Tables 3 to 5 corresponding to the second to fourthembodiments, respectively.

                  TABLE 3                                                         ______________________________________                                        (Embodiment 2)                                                                (f - 33.00)  Diopter = 0.0  Magnification = 1.75                              Radius of      Axial     Refractive Abbe                                      Curvature      Distance  Index      Number                                    ______________________________________                                                   r.sub.16                                                                             ∞                                                                              d.sub.16'                                                                          11.5                                            P'                                 N.sub.9                                                                            1.62588                                                                             ν.sub.9                                                                        35.70                                  r.sub.17'                                                                            ∞                                                                              d.sub.27                                                                           22.0                                                       r.sub.28*                                                                             20.000                                                                              d.sub.28                                                                           4.0                                             L.sub.14                           N.sub.15                                                                           1.49140                                                                             ν.sub.15                                                                       57.9                                   r.sub.29*                                                                            -20.000                                                                              d.sub.29                                                                           17.0                                                       r.sub.30                                                                             ∞                                                                              d.sub.30                                                                           4.0                                             G                                  N.sub.16                                                                           1.49140                                                                             ν.sub.16                                                                       57.9                                   r.sub.31                                                                             ∞                                                                              d.sub.31                                                                           58.0                                                       r.sub.32                                                                              27.000                                                                              d.sub.32                                                                           3.0                                             L.sub.15                           N.sub.17                                                                           1.61762                                                                             ν.sub.17                                                                       52.70                                  r.sub.33                                                                             -10.700                                                                              d.sub.33                                                                           1.0                                             L.sub.16                           N.sub.18                                                                           1.73300                                                                             ν.sub.18                                                                       28.24                                  r.sub.34                                                                             -30.000                                                                              d.sub.34                                                                           71.3                                                       r.sub.35*                                                                             20.000                                                                              d.sub.35                                                                           4.0                                             L.sub.17                           N.sub.19                                                                           1.49140                                                                             ν.sub.19                                                                       57.9                                   r.sub.36*                                                                            -20.000                                                                              d.sub.36                                                                           27.0                                            Eye Point                                                                     ______________________________________                                         *ε = -1.25, iΣ Ciφ.sup.2i = 0                          

                  TABLE 4                                                         ______________________________________                                        (Embodiment 3)                                                                (f = 33.00)  Diopter = 0.0  Magnification = 1.94                              Radius of      Axial     Refractive Abbe                                      Curvature      Distance  Index      Number                                    ______________________________________                                                   r.sub.16                                                                             ∞                                                                              d.sub.16'                                                                          11.5                                            P'                                 N.sub.9                                                                            1.62588                                                                             ν.sub.9                                                                        35.70                                  r.sub.17'                                                                            ∞                                                                              d.sub.27                                                                           18.0                                                       r.sub.28*                                                                             20.000                                                                              d.sub.28                                                                           4.0                                             L.sub.14                           N.sub.15                                                                           1.49140                                                                             ν.sub.15                                                                       57.9                                   r.sub.29*                                                                            -20.000                                                                              d.sub.29                                                                           16.8                                                       r.sub.30                                                                             ∞                                                                              d.sub.30                                                                           4.0                                             G                                  N.sub.16                                                                           1.49140                                                                             ν.sub.16                                                                       57.9                                   r.sub.31                                                                             ∞                                                                              d.sub.31                                                                           20.1                                                       r.sub.32*                                                                             20.000                                                                              d.sub.32                                                                           4.0                                             L.sub.15                           N.sub.17                                                                           1.49140                                                                             ν.sub.17                                                                       57.9                                   r.sub.33*                                                                            -20.000                                                                              d.sub.33                                                                           34.0                                                       r.sub.34*                                                                             20.000                                                                              d.sub.34                                                                           4.0                                             L.sub. 16                          N.sub.18                                                                           1.49140                                                                             ν.sub.18                                                                       57.9                                   r.sub.35*                                                                            -20.000                                                                              d.sub.35                                                                           39.0                                                       r.sub.36*                                                                             20.000                                                                              d.sub.36                                                                           4.0                                             L.sub.17                           N.sub.19                                                                           1.49140                                                                             ν.sub.19                                                                       57.9                                   r.sub.37*                                                                            -20.000                                                                              d.sub.37                                                                           20.0                                            Eye Point                                                                     ______________________________________                                         *ε = -0.95, iΣ Ciφ.sup.2i = 0                          

                  TABLE 5                                                         ______________________________________                                        (Embodiment 4)                                                                (f = 33.00)  Diopter = 0.0  Magnification = 1.95                              Radius of      Axial     Refractive Abbe                                      Curvature      Distance  Index      Number                                    ______________________________________                                                   r.sub.16                                                                             ∞                                                                              d.sub.16'                                                                          11.5                                            P'                                 N.sub.9                                                                            1.62588                                                                             ν.sub.9                                                                        35.70                                  r.sub.17'                                                                            ∞                                                                              d.sub.27                                                                           18.0                                                       r.sub.28*                                                                             16.000                                                                              d.sub.28                                                                           4.0                                             L.sub.14                           N.sub.15                                                                           1.49140                                                                             ν.sub.15                                                                       57.9                                   r.sub.29                                                                             -30.000                                                                              d.sub.29                                                                           40.1                                                       r.sub.30                                                                              30.000                                                                              d.sub.30                                                                           4.0                                             L.sub.15                           N.sub.16                                                                           1.49140                                                                             ν.sub.16                                                                       57.9                                   r.sub.31*                                                                            -16.000                                                                              d.sub.31                                                                           41.8                                                       r.sub.32*                                                                             16.000                                                                              d.sub.32                                                                           4.0                                             L.sub.16                           N.sub.17                                                                           1.49140                                                                             ν.sub.17                                                                       57.9                                   r.sub.33                                                                             -30.000                                                                              d.sub.33                                                                           40.1                                                       r.sub.34                                                                              30.000                                                                              d.sub.34                                                                           4.0                                             L.sub.17                           N.sub.18                                                                           1.49140                                                                             ν.sub.18                                                                       57.9                                   r.sub.35*                                                                            -16.000                                                                              d.sub.35                                                                           20.0                                            Eye Point                                                                     ______________________________________                                         *ε = -0.85, iΣ Ciφ.sup.2i = 0                          

In these embodiments, the object side part 1 (r₁ to r₁₅) of theobjective lens system and the air space d₁₅ in the finder system areidentical with those in the first embodiment, and not shown, but thebranch optical system is only shown. Further, in FIGS. 4 to 6, theelements of the branch optical system are shown along a straight opticalaxis equivalent to the practical optical axis including reflection onmirrors. It should be noted that the embodiments in FIGS. 5 and 6 areeach formed by identically shaped single lenses. Further, in case of theFIG. 5 embodiment, each single lens is symmetrically shaped. Inaddition, the focusing plate G having a reticle on its image sidesurface is located at the position of the primary real image in case ofFIGS. 4 and 5 embodiments as indicated by 9'. FIGS. 11a to 11c, 12a to12c, and 13a to 13c correspond to the second to fourth embodiments,respectively. Necessary data for the longitudinal chromatic aberrationof F-line to 3-line of the second to fourth embodiments are summarizedin the following table with those of the first embodiment and theexemplary prior art.

    ______________________________________                                        Object        Whole                                                           Side Part     Ob-                     At                                      of            jective Branch   Whole  Reticle                                 Objective     lens    Optical  Finder of Finder                               Lens System   system  System   System System                                  (diopter)     (mm)    (diopter)                                                                              (diopter)                                                                            (mm)                                    ______________________________________                                        1st emb.                                                                             -0.43       0.026  0.55   -0.07   0.030                                2nd emb.                                                                             "          "       0.78   0.43   -0.043                                3rd emb.                                                                             "          "       2.17   1.75   -0.043                                4th emb.                                                                             "          "       2.12   1.69   --                                    Prior Art                                                                             0.23      -0.043  -0.39  -0.023 -0.049                                ______________________________________                                    

The above table discloses that a simplified branch optical system ofinsufficient correction of longitudinal chromatic aberration can besuccessfully utilized to form a high class of finder system inaccordance with the present invention.

By the way, the objective lens system in FIGS. 2 and 3 are zoom lenssystems, and the position in the Figures or Tables 1-L, 1-F, 2-l, and2-F are of telephoto position. In case of wide angle photography, d₆=0.7, d₁₂ =17.0, d₁₅ =7.1 and f=8.73 in Table 1-L and 1-F, while d₆-0.7, d₁₂ =17.0, d₁₄ -9.1 and f-8.74 in Tables 2-L and 2-F. In FIGS. 2and 3, the focusing lens group, the variator lens group, the compensatorlens group, and the relay group are identified with F, V, C and R,respectively.

What is claimed is:
 1. An optical system for use in single lens reflexcameras comprising:an objective lens system consisting of an object sidepart with its longitudinal chromatic aberration of F-line to d-linebeing overcorrected to provide a negative value in diopters, and animage side part of a positive refractive power with its longitudinalchromatic aberration of F-line to d-line being undercorrected to providea negative value in millimeters, an image forming light path beingpassed through the object side and image side parts toward the image,whereby the undercorrected longitudinal chromatic aberration of theimage side part is substantially cancelled with the overcorrectedlongitudinal chromatic aberration of the object side part; means forbranching the image forming light path between the object side part andthe image side part of the objective lens system; and a branch opticalsystem of a positive refractive power with its longitudinal chromaticaberration of F-line to d-line left in an undercorrected condition, toprovide a positive value in diopters, the branch optical systemreceiving the branched light path to form a finder system in combinationwith the object side part of the objective lens system, whereby theundercorrected longitudinal chromatic aberration of the branch opticalsystem is predetermined in a complimentary manner to be substantiallycancelled by the overcorrected longitudinal chromatic aberration of theobject side part of the objective lens system.
 2. The invention of claim1, wherein the absolute value of the overcorrected longitudinalchromatic aberration of the object side part of the objective lenssystem is over 0.3 diopter in terms of finder.
 3. The invention of claim1, wherein the branched light path receiving optical system includes atleast one lens element having at least one aspherical surface.
 4. Theinvention of claim 3, wherein the branched light path receiving opticalsystem includes, from the object to eye side, a front lens groupconsisting of a doublet, an intermediate lens group consisting of a pairof single lenses, and a rear lens group consisting of a doublet.
 5. Theinvention of claim 4, wherein the pair of single lenses in theintermediate lens group are identically shaped lenses formed bysymmetric aspherical surfaces.
 6. The invention of claim 4, wherein thebranched light path receiving optical system further includes a focusingplate located between the intermediate and rear lens groups.
 7. Theinvention of claim 3, wherein all the optical elements, which sharerefractive powers of the branched light path receiving optical system,consist of identically shaped single lenses.
 8. The invention of claim7, wherein each of the optical elements is symmetrically shaped.
 9. Theinvention of claim 3, wherein the branched light path receiving opticalsystem includes, from the object to eye side, a front lens groupconsisting of a single lens, an intermediate lens group, and a rear lensgroup consisting of a single lens identically shaped with the singlelens in the front lens group.
 10. The invention of claim 9, wherein theintermediate lens group consists of a doublet.
 11. The invention ofclaim 1, wherein the object side part of the objective lens systemincludes at least one movable lens group for zooming operation.
 12. Theinvention of claim 11, wherein the object side part of the objectivelens system includes, from the object to image side, a focusing lensgroup, variator lens group and a compensator lens group.
 13. Theinvention of claim 12, wherein the compensator lens group includes adoublet for causing the overly corrected longitudinal chromaticaberration.
 14. An optical system for use in single lens reflex camerascomprising:an object lens system including an object side part and animage side part, an image forming light path being passed through theobject side and image side parts toward the image; means for branchingthe image forming light path between the object side part and the imageside part of the objective lens system; and a branch optical system forreceiving the branched light path to form a finder system in combinationwith the object side part of the objective lens system, wherein, theimage side part of the object lens system and the branch optical systemeach have a positive refractive power and correspondingly an inherentlongitudinal chromatic aberration, the inherent aberration being left inan undercorrected condition to simplify both the lens construction ofthe image side part of the objective lens system with its longitudinalchromatic aberration of F-line to d-line represented by a negative valuein milliters and the branch optical system with its longitudinalchromatic aberration of F-line to d-line represented by a positive valuein diopters and wherein the object side part of the objective lenssystem has an overcorrected longitudinal chromatic aberration of F-lineto d-line represented by a negative value in diopters, which is oppositeto the inherent aberration of the image side part of the object lenssystem and the branch optical system to cancel them with it, whereby,the whole lens construction of the optical system for use in single lensreflex cameras is simplified with the correction of the longitudinalchromatic aberration achieved.
 15. A combination objective lens systemand viewfinder wherein the objective lens system transmits an image withsignificant aberration to the viewfinder, the viewfinder capable ofcorrecting the aberration and being defined as follows;

    ______________________________________                                        (f = 33.00)  Diopter = 0.0  Magnification = 1.75                              Radius of      Axial     Refractive Abbe                                      Curvature      Distance  Index      Number                                    ______________________________________                                                   r.sub.16                                                                             ∞                                                                              d.sub.16'                                                                          11.5                                            P'                                 N.sub.9                                                                            1.62588                                                                             ν.sub.9                                                                        35.70                                  r.sub.17'                                                                            ∞                                                                              d.sub.27                                                                           22.0                                                       r.sub.28*                                                                             20.000                                                                              d.sub.28                                                                           4.0                                             L.sub.14                           N.sub.15                                                                           1.49140                                                                             ν.sub.15                                                                       57.9                                   r.sub.29*                                                                            -20.000                                                                              d.sub.29                                                                           17.0                                                       r.sub.30                                                                             ∞                                                                              d.sub.30                                                                           4.0                                             G                                  N.sub.16                                                                           1.49140                                                                             ν.sub.16                                                                       57.9                                   r.sub.31                                                                             ∞                                                                              d.sub.31                                                                           58.0                                                       r.sub.32                                                                              27.000                                                                              d.sub.32                                                                           3.0                                             L.sub.15                           N.sub.17                                                                           1.61762                                                                             ν.sub.17                                                                       52.70                                  r.sub.33                                                                             -10.700                                                                              d.sub.33                                                                           1.0                                             L.sub.16                           N.sub.18                                                                           1.73300                                                                             ν.sub.18                                                                       28.24                                  r.sub.34                                                                             -30.000                                                                              d.sub.34                                                                           71.3                                                       r.sub.35*                                                                             20.000                                                                              d.sub.35                                                                           4.0                                             L.sub.17                           N.sub.19                                                                           1.49140                                                                             ν.sub.19                                                                       57.9                                   r.sub.36*                                                                            -20.000                                                                              d.sub.36                                                                           27.0                                            Eye Point                                                                     ______________________________________                                         *ε = -1.25, iΣ Ciφ.sup.2i = 0                          

wherein p', L₁₄, G, L₁₅, L₁₆, and L₁₇ represent elements in theviewfinder lens system and r_(x*) represents aspherical surfaces.
 16. Animproved optical system for use in a camera having a primary object lenssystem for forming an image on a recording member and a secondaryviewfinder lens system for observing the object scene to be recorded,comprising:at least one first lens group common to the primary objectivelens system and to the secondary viewfinder lens system with apredetermined overcorrection of longitudinal chromatic aberration ofF-line to d-line represented by a negative value in diopters; a secondrelay lens group optically aligned with the first lens group fortransmitting an image of the object scene to the recording member, thesecond relay lens has a chromatic aberration of negative value inmillimeters, the absolute value of which is greater than 0.0004f_(R) forthe F-line to d-line to compensate the overcorrection of the first lensgroup and to provide an acceptable image resolution; a third viewfinderrelay lens group on the image side of the first lens group fortransmitting an image of the object scene to a viewer, the thirdviewfinder relay lens group has a predetermined undercorrection oflongitudinal chromatic aberration of F-line to d-line represented by apositive value in diopters to compensate the overcorrection of the firstlens group and to provide an acceptable image to the viewer, and meansfor optically transmitting an image forming light path to the thirdviewfinder relay lens system, wherein f_(r) represents the focal lengthof the second relay lens group.
 17. The invention of claim 16 whereinthe absolute value of the overcorrected longitudinal chromaticaberration of the first lens group is over 0.3 diopter in terms of theviewfinder.
 18. The invention of claim 16 wherein the light pathreceiving viewfinder relay lens system includes at least one lenselement having at least one aspherical surface.
 19. An improved opticalsystem for use in a camera having a primary objective lens system forforming an image on a recording member and a secondary viewfinder lenssystem for observing the object scene to be recorded, comprising:atleast one first lens group common to the primary objective lens systemand to the secondary viewfinder lens system with a predeterminedovercorrection of longitudinal chromatic aberration of F-line to d-lineto provide a negative diopter value; a second relay lens group opticallyaligned with the first lens group for transmitting an image of theobject scene to the recording member, the second relay lens has apredetermined undercorrection of longitudinal chromatic aberration sothat the aberration of the F-line to d-line is of a negative value inmillimeters, in order to match the overcorrection of the first lensgroup and to provide an acceptable image resolution; a third viewfinderrelay lens group on the image side fo the first lens group fortransmitting an image of the object scene to a viewer, the thirdviewfinder relay lens group has a predetermined undercorrection oflongitudinal chromatic aberration of F-line to d-line to provide anacceptable image to the viewer, and means for optically transmitting animage forming light path to the third viewfinder relay lens system.